AMENDMENT TO LICENSE AGREEMENT

     This Amendment to License  Agreement,  dated as of 31st October 1997, is by
and among Applied Research Systems ARS Holding N.V. ("ARS"); Laboratoires Serono
S.A. ("LSA"), the successor in interest to Serono Diagnostic S.A. ("Diagnostic")
(ARS,  LSA and any  successor  thereof  being  collectively  referred  to as the
"Serono Companies") and Quantech Ltd. ("Quantech"), the successor in interest to
Spectrum Diagnostics, S.p.A. ("Spectrum").

RECITALS:

A.       The Serono Companies and Quantech are parties to the License, 
         Sublicense  and Purchase  Agreement dated November 7th, 1991, attached
         as Exhibit A (the "License Agreement").

B.       Section 2 (a) (i) of the License  Agreement  reserves from the scope of
         the license granted to Spectrum thereunder, among other reservations, a
         right  to  develop  and   commercialize  the  SPR  technology  for  the
         development  of  products  to be  marketed  in the  name of the  Serono
         Companies and/or Serono Affiliates (the "SPR License Reservation").

C.       Section  2 (d)  of  the  License  Agreement  sets  forth  a  series  of
         benchmarks of aggregate payments (the "Minimum  Royalties") and Section
         4(b) of the License  Agreement  sets forth  sublicense,  assignment and
         transfer royalties (the "Transfer Royalties").

D.       Section 2 (e) of the License  Agreement grants the Serono Companies and
         Serono  Affiliates the right to demand a royalty-free  right to use any
         technology  Spectrum has developed with respect to SPR (the "Grant Back
         License"), subject to certain reservations.

E.       Upon an Event of  Default,  Section 10 of the  License  Agreement  (the
         "Default  Provision")  provides  that the  license  rights  granted  to
         Spectrum shall terminate and revert back to the Serono Companies.

F.       The Serono Companies and Quantech wish to amend and restate the License
         Agreement  as it  concerns  the SPR  License  Reservation,  the Minimum
         Royalties,  the Transfer  Royalties,  the Grant Back  License,  and the
         Default Provision.



In consideration of the agreements  contained herein and other good and valuable
consideration,  the  sufficiency  of which is hereby  acknowledged,  the parties
agree as follows:

1.       Definitions.  All of the defined  terms in the License  Agreement shall
         have the same  meanings in this Amendment to License Agreement.

2.       SPR License Reservation.  Upon Payment to the Serono Companies pursuant
         to Section  2(d) of the License  Agreement  of Minimum  Royalties of at
         least  $1,000,000  in the  aggregate by December  31, 1997,  the Serono
         Companies,  on behalf of themselves  and the Serono  Affiliates,  shall
         waive all of their rights under the SPR License Reservation.


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3.       Minimum Royalties.  Section 2 (d) of the License Agreement shall be 
         amended to read as follows:

                  (d) Minimum Royalty:  Notwithstanding  anything stated in this
         Agreement  to the  contrary,  in the event  that the  royalty  payments
         actually  paid to the Serono  Companies  by  Spectrum  and/or any Third
         Party  Transferee  pursuant to Section 4 of this Agreement do not equal
         the  following  amounts:  (a) at least  $500,000  in the  aggregate  by
         December 31, 1993;  (b) at least  $850,000 in the aggregate by December
         31,1995; (c) at least $1,000,000 in the aggregate by December 31, 1997;
         (d) at least $1,150,000 in the aggregate by December 31, 1998;  and (e)
         at least  $1,300,000 in the  aggregate by December 31, 1999,  then each
         time  one of the  first  three  of  such  benchmarks  is not  met,  the
         cumulative  royalties  to be paid to the Serono  Companies  pursuant to
         Section  4(d) hereof  shall be  increased  by two million  ($2,000,000)
         dollars  so that if all  three  initial  benchmarks  are not  met,  the
         cumulative  royalties  payable  to the  Serono  Companies  pursuant  to
         Section  4(d)  hereof  shall  be  increased   from   eighteen   million
         ($18,000,000)  dollars to twenty-four  million  ($24,000,000)  dollars.
         Also if any one of the first  three of such  benchmarks  is not met the
         restrictions on the Serono Companies pursuant to Section 2(a)(i) hereof
         that provide only the Serono Companies  and/or Serono  Affiliates shall
         be allowed to market  products  developed  pursuant to the retention of
         the right to develop and  commercialize  SPR shall  lapse.  If Spectrum
         shall  receive  any lump sum payment  from any Third  Party  Transferee
         under a Transfer  Agreement  prior to December 31, 1999,  then Spectrum
         shall  accelerate  payment of the minimum  royalties  set forth in this
         Section  2(d) by  paying up to  twenty  percent  (20%) of such lump sum
         payment to the Serono Companies.  It is expressly  understood that such
         lump  sum  payments  do  not  give  rise  to  any  additional   royalty
         obligations  than would  otherwise  be payable to the Serono  Companies
         under  Section  4(b) and  shall  not  increase  any  aggregate  minimum
         royalties payable under this Section 2(d).

4.       Section 4(b)(B) of the License Agreement shall be restated to read as
         follows:

                  (B)  Commencing on July 2, 1996,  each Third Party  Transferee
         shall  pay  Third  Party  Royalties  to  Diagnostic  equal  to the  15%

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         Royalties.  The obligation of Spectrum and any  subsequent  Third Party
         Transferees to pay Third Party Royalties to the Serono  Companies shall
         terminate only in accordance with subparagraph 4(d) below.

5.       Grant Back License. Section 2 (e) of the License Agreement shall be 
         amended to read as follows:
      
                  (e)   Spectrum   Obligation   to  provide   technology:   Upon
         termination  of this  Agreement  under  Section  10 below,  the  Serono
         Companies shall be entitled to a royalty-free  license to make, use and
         sell whatever  technology  Spectrum has developed  with respect to SPR,
         provided that such license shall be subject to the terms and conditions
         of any Preferred Transfer Agreement (as that term is defined in Section
         6 of the Amendment to License  Agreement)  which is in force and effect
         at the time of such  termination of this Agreement.  This  royalty-free
         license shall not extend to any  technology  and/or data and/or patents
         which  Spectrum  developed with a third party and with respect to which
         the third party retained a proprietary right.


6.       Default  Provision.  Upon an Event of Default  under the Default  
         Provision,  any  sublicense  granted by Quantech to a Preferred Third 
         Party  Transferee  under a Preferred  Transfer  Agreement prior to the
         Event of Default shall survive  termination of the license and 
         sublicense  rights in the Licensed SPR Technology granted to Spectrum
         and  reversion of such license and  sublicense  rights to the Serono 
         Companies  under the Default  Provision,  and such  Preferred Transfer
         Agreement  shall continue in full force and effect  under  its own 
         terms  and  conditions.  For purposes of this Section 6, a  "Preferred
         Third  Party Transferee"  shall be any third  party  which had  assets
         of $100  million or more at the end of the third party's  fiscal year
         immediately  preceding  the execution of such  Transfer  Agreement.  
         For purposes of this Section 6, a "Preferred  Transfer  Agreement"
         shall be any Transfer Agreement with a Preferred Third Party Transferee
         which is approved by LSA, which approval will not be unreasonably 
         withheld.


7.       Execution in Counterparts.  This Amendment to License  Agreement may be
         executed in one or more counterparts,  all of which shall be considered
         one and the same agreement,  and shall become a binding  agreement when
         one or more  counterparts  have been signed by each party and delivered
         to the other party.




<PAGE>


IN WITNESS  WHEREOF,  the parties  hereto have duly executed and delivered  this
Amendment to License Agreement as of the date first above written.

APPLIED RESEARCH SYSTEMS            LABORATOIRES SERONO S.A.
 ARS HOLDING N.V.


/s/ Reginald Schotborgh
/s/ S. Antonius-Soedhoe
                                    /s/ T.P. Verhassee
By Reginald Schotborgh/             By T.P. Verhassee
   S. Antonius-Soedhoe                
Its Managing Directors              Its Senior Vice President of Operations




QUANTECH LTD.
                                     /s/ Jacques Theurillat
                                     By Jacques Theurillat
                                     Its Director
/s/ Gregory G. Freitag
By Gregory G. Freitag

Its COO and CFO